This invention relates to a carrier roller made of synthetic resin and used for supporting a conveyor belt, which roller has a function of discharging static electricity.
Rollers for a belt-conveyor have conventionally been made of metals, rubbers, or plastics; rollers used in the construction work or civil engineering field are mostly made of a metal because of its large strength, less wearing, or long durability. Further reason for that is that there is little likelihood of electrostatic charging and where is good conduction of generated electricity. Metallic rollers are, however, troubled by some unavoidable defects, such as, operation noise and relatively large rotation resistance due to their heavy weight. It consequently causes a large power consumption and increasing cost in equipment manufacture as well as in operation.
For the purpose of eliminating the abovementioned disadvantages, synthetic resin- or rubber-made rollers have been widely employed. These materials provided again a new problem of electrostatic charging on the surface of the rollers, because they are very high in the insulation resistance of electricity. Friction between the rubber belt and the rollers of synthetic resin or rubber is liable to generate static electricity, which often causes a spark by any chance. Unexpected sparking often gives rise to a fire which may develop into a great damage.
Static electricity charging has loomed large in the art, which should be solved by all means. A few anti-charging attempts have been made. Painting of an anti-charging paint was tried in vain, because of its short life, having no stable and durable effect. Using a filler of conductor materials, such as a mixture of carbon black pigment and plastic pellets, for the roller was also proposed, but did not become popular because of its high wearing rate. No decisive anti-charging roller has been introduced so far.